Many Longhorn cattle sunbathe in Tres Hermanos Ranch, a 2,450-acre preserve owned by City of Industry, between Diamond Bar and Chino Hills on Monday, Nov. 7, 2016, is up for sale. (Photo by Watchara Phomicinda, San Gabriel Valley Tribune/ SCNG)

Diamond Bar, Chino Hills and the City of Industry are negotiating a joint partnership that would give each city partial control over the 2,500-acre Tres Hermanos Ranch, one of the largest swaths of open space left in the region, according to sources close to the discussions.

Late last month, Diamond Bar and Chino Hills agreed to freeze their lawsuits against Industry for 90 days to give the parties more time to negotiate, court records showed.

If an agreement is reached, it would put an end to years of fighting over the property, which is owned by Industry but situated within Diamond Bar and Chino Hills’ jurisdictions. Tres Hermanos has avoided development for decades and is still used for grazing cattle, including longhorns.

That almost changed when Industry unveiled plans to develop a solar farm on the land, despite objections from the other two cities.

But now, after two years and millions of dollars invested in the project, the solar farm idea is dead, and sources say the three parties are close to reaching a mutually beneficial agreement. The sources are not identified because the settlement negotiations are confidential.

“Everybody is pretty much on the same page,” a source said. “But it’s still a work in progress.”

If the negotiations pan out, the three cities would form a joint powers authority, and that group, made up of council members from each city, would control Tres Hermanos. Among the hurdles is the $42 million price tag on the ranch land. Industry won the right to buy the land back from its redevelopment agency last year, but the sale never finalized because of the litigation.

It’s unclear how the new partnership would divvy up that cost if Industry decides it no longer wants to foot the whole bill.

Officials in Chino Hills and Industry would not discuss the possibility of a partnership, but they did confirm the ongoing negotiations. Diamond Bar City Manager Dan Fox could not be reached for comment.

Chino Hills City Manager Rad Bartlam would not discuss the specifics of the negotiations, but described the conversations as encouraging and “genuine.” He said he was initially hesitant because of Chino Hills’ strained relationship with Industry’s previous administration.

“The talks have been going on for a number of weeks; we continue to make progress toward an outcome that hopefully we can all live with,” he said.

Industry City Attorney Jamie Casso declined to comment about the negotiations.

Industry’s proposal for a 450-megawatt solar project has become a black eye for the city. The City Council loaned the developer $20 million and could now lose every cent. Industry subpoenaed the developer, San Gabriel Valley Water and Power, last month to force the company to turn over studies and planning documents funded with the loans. So far, the city has received only related maps, images and simple weather data, officials said.

Industry has attempted to end its lease agreement with the developer, but the company is contesting the termination.

“I lost confidence in the project and the money that was being spent without any oversight,” Industry Councilman Newell Ruggles said. He agreed that Diamond Bar and Chino Hills deserve a say in the future of Tres Hermanos.

“We’re open to any ideas that ensure it’s used for a public purpose,” he said.

Some Industry council members still support the idea of using Tres Hermanos for green energy. Ruggles said he isn’t opposed to a different energy project, though he believes at least some of the land should be open to the public for hiking trails or other uses.

By conceding some control to Diamond Bar and Chino Hills, Industry would repair its damaged relationships and could face less opposition if another project materializes. Perhaps more importantly, it would also put an end to six lawsuits filed by those two cities alleging Industry violated environmental, planning and public records laws while moving forward with the solar farm project.

Not everyone is optimistic about the potential partnership. Jim Gallagher, a member of the group Save Tres Hermanos Ranch, already was aware about a potential joint powers authority when reached by a reporter Friday. He is worried pressure to meet a housing needs assessment could force Diamond Bar and Chino Hills to consider new homes on Tres Hermanos. Residents fear new development could increase traffic and harm the environment.

“There is potential for all three cities to carve out what they want there,” he said. “I am concerned what the outcome could be.”

Gallagher said Save Tres Hermanos Ranch is committed to keeping the property open as part of the natural corridor to protect the fauna, flora and rural atmosphere for residents.

“We can’t just fill up everything with development,” Gallagher said. “We’re going to have to come up with smarter ways to meet our housing needs and preserve our quality of life.”

Jason Henry is an investigative reporter with the Southern California News Group. Raised in Ohio, Jason began his career at a suburban daily near Cleveland before moving to California in 2013. He is a self-identified technophile, data nerd and wannabe drone pilot.